// 获取屏幕快照

     private func screenShot() -> UIImage{

         let window = UIApplication.shared.keyWindow!

         UIGraphicsBeginImageContext(window.size)

         // 绘图

         window.drawHierarchy(in: window.bounds, afterScreenUpdates: false)

         // 从图形上下文获取图片

         let image = UIGraphicsGetImageFromCurrentImageContext()!

         UIGraphicsEndImageContext()

         return image

     }